In a plasma display panel (hereinafter referred to as a “PDP”), ultraviolet rays are generated by discharging gas and exciting phosphor to emit light for a color display. The plasma display panels are classified into two driving systems, i.e., an AC type and a DC type, and classified into two electric discharge systems, i.e., a surface discharge type and an opposed discharge type. The surface discharge type PDP has a three electrode structure is becoming the mainstream in PDPs because of its high resolution, large screen and ease of manufacture. In the three-electrodes-surface-discharge-type PDP mentioned above, pairs of display electrodes, which are parallel to each other, are formed on one substrate. In addition, address electrodes, which cross over the display electrodes, barrier ribs and phosphor layers are disposed on the other substrate. Using this structure, the phosphor layer can be relatively formed thicker, so that the PDP is suitable for a color display using phosphor.
Compared with a liquid crystal panel, the PDP has the following features, namely, a fast motion display, a wide viewing angle, ease of manufacturing a large panel and high quality because of being a self luminous type. As a result, recently, the PDP has drawn attention among flat display panels and has various uses (e.g., a display apparatus at a place where many people gather or a display apparatus for enjoying a large screen image at a home).
A conventional method of manufacturing the PDP is described hereinafter. Constituent elements such as electrodes or a dielectric layer are successively formed on a front substrate and a rear substrate by using a thick film process in which a printing process, a drying process, a firing process and the like are repeated in order. Then the front substrate and the rear substrate are put together and sealed.
In the drying process and the firing process, for example, a plurality of rollers are positioned parallel with each other in a substrate-moving direction so as to form a conveyer. The substrate is dried or fired while it is conveyed by the conveyer. An apparatus mentioned above is called a roller-hearth-sequential-firing apparatus (hereinafter referred to as a “firing apparatus”). Temperature patterns of the firing apparatus are described hereinafter. The substrate is heated to a certain temperature of drying or firing, and kept at the certain temperature for a predetermined time, so that drying or firing is performed. After that, the substrate is cooled.
However, in the conventional manufacturing method discussed above, the substrate tends to become deformed or broken, particularly in a firing process in which the heat load against the substrate is great. When the substrate is conveyed in the firing apparatus, the temperature difference between a front and a back of the substrate is generated in the substrate-moving direction. After that, when the substrate is fired to the firing temperature in just the state it is, the temperature difference becomes greatest in the firing process. As a result, thermal stress is generated, so that the substrate is deformed or broken.
Even when the substrate is not deformed or broken, temperature distribution is generated at the substrate. Therefore, when constituent elements formed on the substrate are dried or fired, a constituent element on the front becomes different from that on the back of the substrate in thermal hysteresis, so that the quality of the constituent elements may be reduced.
When a substrate becomes larger for a large screen or the moving speed becomes faster for high throughput, the problems discussed above become more conspicuous.
The present invention is directed to solve the problems discussed above, and aims to provide a method of manufacturing a PDP, where the temperature difference between a front and a back of a substrate is not generated in a substrate-moving direction, and a firing apparatus used for manufacturing the PDP.